Volume 1

The chemical constitution of the proteins / by R.H.A. Plimmer.

  • Plimmer, Robert Henry Aders, 1877-1955.
Date:
1912-1913
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The chemical constitution of the proteins / by R.H.A. Plimmer. Source: Wellcome Collection.

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    together was described by Morner in 1901. The protein—hair, keratin from horn, egg-shells, etc.—was boiled with five times its quantity of 13 per cent, hydrochloric acid under a reflux condenser on a water- bath for six to seven days. The solution was then decolorised with charcoal and evaporated in vacuo^ and the residue dissolved in 60- 70 per cent, alcohol. The two acids then crystallised out on neutralis- ing with soda, and were separated by fractional crystallisation from ammonia; if much tyrosine was present it separated out first, but if cystine exceeded tyrosine in quantity this compound crystallised out first; the remainder was only separated with difficulty. Embden separated the mixture of the two acids by means of very dilute nitric acid, in which tyrosine is very easily soluble, but cystine with difficulty. Their separation may also be effected by precipitation with mer- curic sulphate in 5 per cent, sulphuric acid solution in which the mercury compound of tyrosine is soluble (Hopkins and Cole). Winterstein, in 1901, showed that cystine was precipitated by phosphotungstic acid, but the observation seems to have been over- looked. Cystine and tyrosine are best separated by means of this reagent. The mixture is dissolved in 5 per cent, sulphuric acid and treated with excess of phosphotungstic acid solution. Cystine phos- photungstate generally separates out in a crystalline condition. From this precipitate the cystine can be obtained by the usual method (see under diamino acids), but a large excess of baryta must be avoided as cystine is readily decomposed by alkalies. Cystine crystallises out on neutralising the filtrate from the barium phosphotungstate. Winter- stein decomposed the phosphotungstate with hydrochloric acid. The precipitate is made into a paste with water, placed in a separating funnel and treated with small quantities of concentrated hydrochloric acid. Ether is added and the mixture well shaken. At first an emulsion is formed, but on adding more ether and acid and thoroughly shaking a clear ethereal solution of phosphotungstic acid settles to the bottom ; if this does not occur, decomposition is not complete and more acid must be added and the shaking repeated. The middle layer containing the cystine hydrochloride is separated ; the other layers are treated once more in the same way and the middle layers are combined. Ether is removed from the acid solution by warming on the water- bath and the cystine is separated by exactly neutralising with soda. Folin prepares cystine from wool by boiling it with concentrated hydrochloric acid in the proportion of 100 grammes wool to 200 c.c.